In much the same way that we can use a few letters to make thousands of words, we can use a few types of atoms to construct all matter. For example, consider the atoms hydrogen, oxygen, and carbon,Notice that we represent atoms by using spheres. We get this idea from the highly magnified pictures of metals that show the atoms.We can combine the hydrogen, oxygen, and carbon atoms in a variety of ways. Just as letters combine to form different words, atoms combine to form different compounds. Compounds are substances made by bonding atoms together in specific ways. These substances contain two or more different types of atoms bound together in a particular way. A specific compound consists of the same particles thoroughout.Consider a glass of water. If you could magically travel inside the water and examine its individual parts, you would see particles consisting of two hydrogen atoms bounded to an oxygen atom.We call this particle a molecule. A molecule is made up of atoms that are "stuck" together. A glass of water, for example, contains a huge number of molecules packed closely together.Carbon dioxide is another example of a compound. For example, "dry ice"-solid carbon dioxide-contains molecules.Notice that the particles (molecules) in water are all the same. Likewise, all the molecules in dry ice are the same. However, the molecule in water differ from the molecules in dry ice. WWater and carbon dioxide are different compounds.
Two years ago I moved to a new neighbourhood. There seem to be very few people in this area who are without telephones, so I expected to get a new phone quickly. I applied for one as soon as I moved into my new house. "We aren't supplying many new phones in your area," an engineer told me. "A lot of people want new phones at the moment and the company is employing fewer engineers than last year so as to save money. A new phone won't cost you mush money, but it will take a little time. We can't do anything for you before December." You nees a lot of patience if you're waiting for a new phone and you need a few friends whose phones you can use as well. Fortunately, I had both. December came and went, but there was no sign of a phone. I went to the company's local to protest. "They told me I'd have a phone by December," I protested. "Which year?" the assistant asked.